1. Field of the Invention
This invention relates to new and improved refrigeration systems and more particularly to a system having a pre-cooler heat exchanger for sub-cooling the liquid refrigerant before entering into the evaporator.
2. Description of the Prior Art
It is well known in the art of refrigeration to improve efficiency by pre-cooling the liquid refrigerant flowing from the condenser to the receiver or flowing directly to the evaporator. Heat exchangers are employed in refrigeration systems for the exchange of heat between fluids, generally the cold refrigerant gases from the evaporator and warm liquid refrigerant from the condenser. The refrigerant gas which is exhausted from the evaporator of the refrigeration system is cold. The liquid refrigerant which is drawn from the condenser of a refrigeration system is warm. To improve the efficiency of the refrigeration system, it is desirable to heat exchange the warm liquid with the cold gas. The following patents illustrate the state of the art in pre-cooler technology:
Donovan U.S. Pat. No. 2,797,554 discloses a refrigeration apparatus including a heat interchanger which comprises, a shell construction having a central chamber, a pair of headers, and a partition separating the headers from the central chamber. Tube assemblies are rigidly mounted on the partition with ends opening into the headers to provide a passageway between the headers. Each tube assembly has its central portion contacting the corresponding portions of a plurality of the other tube assemblies to form the walls of fluid passageways extending longitudinally along the outer surfaces of the tube assemblies. Each tube assembly has ends of reduced cross-section spaced from the ends of the adjacent tube assemblies to provide a header zone in the shell at each end of the tube assemblies. Each tube assembly includes internal fins for heat exchange between fluids passing through the tube assemblies and through the central chamber shell externally of the tube assemblies. Means is provided to deliver a gas to one of the headers and to withdraw the gas from the other of the headers, and to deliver a liquid to one of the header zones at one end of the central chamber in the shell and to withdraw a liquid from the other of the header zones.
Boling, U.S. Pat. No. 2,956,419 discloses an arrangement for maintaining stable operation of refrigeration systems having air-cooled condenses throughout wide variations in the temperature of the cooling air. The invention also provides for maintaining stable operation of refrigeration systems having other types of condensers used with cooling towers.
Marlo U.S. Pat. No. 3,082,610 discloses that refrigerant flow controls, such as expansion valves, capillary tubes and the like, operate most efficiently when the fluctuation of the pressures at their inlet and outlet ports are not unduly great; and consequently that it is desirable to control the pressures at the inlet ports of refrigerant flow controls to keep those pressures from falling too low. Where the refrigerant flow controls are used in compression-expansion refrigeration systems, it is desirable to keep the liquid pressures in the receivers of those systems from falling to unduly low levels. With water-cooled condensers, it is easy to keep the liquid pressures in the receivers of those systems from falling too low; but with air-cooled condensers, it is not always easy to keep the liquid pressures in the receivers of those systems from falling too low. Consequently, it is desirable to keep the liquid pressure in the receiver of an air-cooled refrigeration system from falling to too low a level. A method and apparatus are disclosed for maintaining the liquid pressure in the receiver of an air-cooled refrigeration system above a predetermined minimum level.
Bottum U.S. Pat. No. 3,446,032 discloses a liquid-liquid heat exchanger comprising an outer casing and an inner, thermally-conductive casing, each having an inlet and an outlet for fluid. The inner casing may be fluted in the direction of fluid flow to increase the heat transfer surface and to assist in maintaining turbulent flow of refrigerant. A helical coil may be provided on the inner casing. A helically spiralled strip member may be provided within the inner casing.
Hess U.S. Pat. No. 3,851,494 discloses that excessive warming of the compressor input by the heat exchanger that supercools the condenser output may be prevented by a bypass switched in and out by a thermostatic control at the output of the compressor to prevent the final compression temperature from rising to a value at which damage to lubricating materials and flexible hose materials would result. A branching valve or a second expansion valve may be used according to whether the bypass is just around the heat exchanger or around both the heat exchanger and the evaporator.
Johnston U.S. Pat. No. 3,952,533 discloses an energy saving refrigeration system free of the usual winter head pressure controls on the condenser equipment, capable of functioning satisfactorily with two-phase, liquid-gas mixtures of refrigerant inlet flow, there being a pair of valves immediately upstream of the evaporator, one being an expansion valve, and the other being a pressure regulator just upstream of the expansion valve adjusted to maintain a fixed discharge pressure to the expansion valve, this regulator discharge pressure set sufficiently above the evaporator boiling pressure and set sufficiently below the minimum inlet pressure to the pressure regulator.
Wright U.S. Pat. No. 4,359,879 discloses a refrigeration system for cooling and drying hot, moist, compressed air by sub-cooling the liquid refrigerant from the condenser to eliminate all flash gas and render the entire evaporator effective for refrigeration purposes. The heat exchangers for the evaporator and for sub-cooling the liquid refrigerant are constructed of a one-piece finned copper inner cylinder with the routed fin enclosed inside an annular copper shell in which a 0.020-inch clearance exists between the annular copper shell and the fins to allow passage of a stream of air which causes the laminar flow around the routed fin construction to be agitated by eddy diffusion. The use of the novel heat exchanger in the refrigeration system along with the step of sub-cooling the liquid refrigerant is reported to produce a substantial gain in refrigeration without an increased requirement for either power or energy.